Definitely, this is another hook that draws someone in to read/buy your book. Book trailers intend to get the attention of the viewer to buy/read your book. If you're self-publishing, you have to do everything unless you'll hire a professional.
If you want to save money, there are a lot of free tutorial videos and articles online so I guess it's best to do it yourself. Search on Youtube using the book trailers keyword, it's all up to you to decide which video is helpful. It just need a little research for you to come up with a good and effective book trailer. It's best if you keep it simple, too much unnecessary details will draw the viewers away. An example of a simple yet concise book trailer is Lane Smith's It's a Book, I had fun watching it :-). It's simple yet conveys the essence of the video without giving too much away. It's more fun and easy to make book trailers with Children's book though.
How about you? What do you think about book trailers?